# Witt and cohomological invariants of Witt classes

@article{Garrel2020WittAC,
title={Witt and cohomological invariants of Witt classes},
author={Nicolas Garrel},
journal={Annals of K-Theory},
year={2020}
}
• N. Garrel
• Published 5 December 2017
• Mathematics
• Annals of K-Theory
We classify all Witt invariants of the functor $I^n$ (powers of the fundamental ideal of the Witt ring), that is functions $I^n(K)\rightarrow W(K)$ compatible with field extensions, and all mod 2 cohomological invariants, that is functions $I^n(K)\rightarrow H^*(K,\mu_2)$. This is done in both cases in terms of certain operations (denoted $\pi_n^{d}$ and $u_{nd}^{(n)}$ respectively) looking like divided powers, which are shown to be independent and generate all invariants. This can be seen as a…

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